TECH - Hard-tailing an OIF

[flypa38]

When hardtailing a OIF Triumph frame, the rear engine mount area and adjacent frame tubes seem to be a source of trouble as far as finishing. I'm sure there are plenty of other methods of doing this. Here's my solution, still in progress.
After chopping the rear section and welding on the new tail, what's left over looks something like this:



In order to use as many of the original parts possible to keep the cost down, I opted to retain the original rear engine mounts and finish off the tubes somehow. After a FEW MONTHS of dwelling on it, this is what I came up with......
I started by putting a cut down version of the swingarm back in place using the through bolt for decent alignment. I then tack welded it in place where the swingarm pivot meets with the frame and engine mounts. The through bolt can now be removed. Finally I cut the rest of the swingarm off leaving only the tubular parts that the bolt runs through:

Using 3/16"x3" plate steel, I made two gussets next. I'm sure they help as far as strength, but I mostly put them there for better flow of the frame's lines. To create the arc, I simply traced the outline of a grinding wheel, then made straight lines off the arc to where the gussets needed to end.
To figure out how far to trim the remaining frame tube, I eyeballed just about where the center of the arc will be upon installation of the gusset, and cut the tube so that the end pointed about that direction. Next cut a vertical slot in the rear of the remaining tube so that the gusset can be butted against the back of the engine mount. The gusset can now be welded in place like this:



The thing that really stumped me for the longest time was what to do with those tube ends. This is what was settled on. I bought two large acorn nuts, originally intended for the ends of the rear axle. The acorn nuts were cut in half vertically so that each half could be welded to the frame tube and gusset on each side:


Future plans include a bracket for a brake light switch, filling the holes where the swingarm bolt went, and LOTS of finish welding!
That's about it! Unfortunately my photography is just as bad as my welding. Sorry for that, but you get the idea! Hope this helps somebody who is brainstorming like I was for a solution! If you have a question on any of this feel free to PM!
Johnny

[flypa38]

I bought my hard tail section from Rask Cycle in Evans City, PA. He's a local guy and knows just about everything there is to know about British bikes.
So here goes! Obviously, you'll start by cutting off the un-needed parts of the original frame. Suggestions here are to cut the lower tubes above the rear engine mounts, and cut the top tubes (by the oil cap) as close to the oil tank part of the frame as possible without damaging it at all. Most important thing though, is to leave the swingarm in place, and trim a couple inches off, as needed, from the extreme rear.
Alignment is pretty easy, but really important! This mock up shows sort of what I mean in regards to trimming the rear of the swingarm, and by the time everything was matched up, another 2" or so was removed!



Side to side alignment is super easy using the swingarm. After trimming the rear of the swingarm as needed, use it to align the aft part of the tail section:



Height alignment:
When you get everything just about fitted right, the frame will need to be secured to a completely level table or surface. Next, slide something such as a large bolt or round stock through the axle slots. Measure the radius of your rear wheel inlcuding the tire, and get an approximate height that the axle needs to be blocked up to get the ride height you want. For instance, if your real wheel and tire measure 11" from axle center to outside of tire, and you want a 4" ride height, the rear will need to be blocked up 7".



Next, make sure that the tail section is not twisted in relation to the original part of the frame. Using a level, check to see that the original frame is level in front of the down tube/oil tank, and the tail section is level where it meets the original frame, and across the axle slots.
Check and re-check everything, and when you're satisfied tack the tail section on and re-check everything. If it stayed aligned, go ahead and finish weld the tail section on.
A word of caution here.....be REALLY careful to not melt through the oil tank portion of the original frame when welding. Even with a really precisely controlled TIG we managed to burn mine through in a couple tiny spots and filling those holes with the little bit of oil contamination from inside the frame was a royal pain!
Finished result is long n' lean and I sure like how it turned out!



For finishing of the rear engine mount and removal of the swingarm, see my other tech post:
http://www.jockeyjournal.com/forum/s...+mount+tidying

Hope this helps somebody!
Johnny

[hatch]

I have a couple more ideas if you are interested....After trimming the swingarm, I weld some heavy flat stock on the inside axle adjusting area and it then becomes a dedicated fixture. Also, I use a household lazer level, and a steel ruler for checking alignment....cheap insurance for backyard building.

[flypa38]

Awesome idea Hatch! The tail section I got was really straight, and the level worked well, but nothin' beats a laser for a straight line!

[Neo Dutch]

Looks nice. I have read that OIF may not be structually sound when hardtailed in this manner. You may want to look at some gussets to distribute the forces placed on the backbone by the seat rails. An added bonus would be somewhere to put a seat hinge.

[chopaweeza]

I've read and seen the same thing Dutch. A well known Sydney shop did a beautiful weldon hardtail on a T140 frame about 10 years ago. A number of Sydney siders will remember it from the shows in the late 90's. The re-worked frame had 6-7000kms on it and suffered structural failure were the tubes attached to the spine. The tubes & welds didn't fail but the original spine wall tore out with the seat rails & welds still intact. Saw the bike when it was taken to a frame repairer. The repairer , Aldertons, who have been repairing frames for over 30 years refused to repair it as it would just keep happening. Reason they gave was the wall thickness on the oil baring spine was too thin to handle the extra stresses placed on that area by a hardtail. Lost track of it after that but the painted tank & front end were at Hawkesbury Swapmeet about 5 years ago. When I was buying rigid frames for import to Australia from the UK in 92' I inspected a number of frames including an OIF that had been hardtailled by Uncle Bunts. Even though Bunts have a solid rep as a quality item normally this one had stress fractures in the same spot that the one in Sydney had only this one hadn't totally failled yet. Ask Pro British Custom Frame Builders and most will tell you it's not a great idea. If you are going to run a frame like this on the road keep a really close eye on those welds and check them regularly. Brace the hell outy of the area to spread the stress load out as well.

[flypa38]

There actually is a triangular piece just behind the oil cap for a a hinge to be mounted to, structurally it helps too. I added it after these pics. I can definately see what you mean as far as that material being thin where the hardtail section meets the spine, but it welds on very near were the rear section of the original frame was welded. Would it be any less strong thean the original? Any ideas on making it a little stronger?
Hatch has done quite a few OIF's I think....any problems encountered?
Thanks!
Johnny

[dixiedog]

Stupid question, what does OIF mean?

[Richard D]

Oil In Frame - The large tube of the frame acts as the oil tank.

[dixiedog]

Thanks - I wondered why the down tube looked so big.

[hatch]

I think a triangle piece also on the bottom, at the point where the tail section connects to the oil tube would also help. Like anything "custom", it's all somewhat of a gamble, but watching for clues of failure is still the best plan on everything custom. Failure of any thing usually gives some hints before it breaks...whether it's a frame, or bracket, or anything structural. I'm not an engineer, so I try to over do strength. Since the top attaching point is in compression, if it fails, danger is minimal.....unlike , for example, a raked neck.

[flypa38]

Hey Hatch,
Do you mean another gusset under where the seat hinge would go?
Also, what amperage. tungsten, filler do you suggest for TIGgin' on that oil tank section of the frame? A buddy of mine welded the tail section on for me on account of I don't trust my TIG skills yet.
Thanks!
Johnny

[scootermcrad]

Glad someone finally did this! Thanks for sharing...